MIPS64: Make --always-opt also optimize top-level code.

MIPS64: Make --always-opt also optimize top-level code.

Port 2d281e71ac49058ef5696f4255ff1fa30796bc5e

Original commit message:
This enables eager optimization of top-level code with TurboFan and
extends test coverage by triggering it with the --always-opt flag.
Script contexts are now also properly allocated in TurboFan.

BUG=

Committed: https://crrev.com/e9224e4ab3089236062f1699e87cfa412aba4360
Cr-Commit-Position: refs/heads/master@{#27643}

[balazs.kilvady, 2015-04-07 18:06:49]

balazs.kilvady@imgtec.com changed reviewers:
+ akos.palfi@imgtec.com, danno@chromium.org, dusan.milosavljevic@imgtec.com,
gergely.kis@imgtec.com, mstarzinger@chromium.org, paul.lind@imgtec.com

[paul.l..., 2015-04-07 19:25:55]

lgtm

[balazs.kilvady, 2015-04-07 20:22:26]

The CQ bit was checked by balazs.kilvady@imgtec.com

[commit-bot: I haz the power, 2015-04-07 20:22:38]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1066843005/1

[commit-bot: I haz the power, 2015-04-07 21:11:11]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-04-07 21:11:25]

Patchset 1 (id:??) landed as
https://crrev.com/e9224e4ab3089236062f1699e87cfa412aba4360
Cr-Commit-Position: refs/heads/master@{#27643}